Our application uses many jar files (31) in the classpath to run. When we started looking into the app's memory footprint, we found that when a Class is attempted to be loaded that doesn't exist in the classpath (so all the jars would be searched for the class), the virtual memory jumped up about 10Meg. If we unjarred all our jars, the memory did not increase. The following is the ps output from running a simple test app that calls ClassLoader.getSystemClassLoader().loadClass("java.text.resources.DateFormatZoneData_en_US"); and then sleeps.

ps -p 10518 -o vsz -o rss (With jars in classpath)
 VSZ RSS
38912 11688

ps -p 10541 -o vsz -o rss (With extracted class files)
 VSZ RSS
28560 7808

This bug may be a duplicate of Bug 4467358, but it appears as though that bug is going to be closed.